Impact of Hydrodynamic Cavitation Pretreatment on Sodium Oleate Adsorption onto Diaspore and Kaolinite Surfaces
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors focused on the effect of preliminary hydrodynamic cavitation of the kaolinite and diaspore suspension for the flotation of these minerals. They investigated the effect of aeration, contact angles as a function of pH and NaOl concentration. They received a distribution of kaolinite from the diaspore.
The paper is generally well-written and the structure well-organized. However, I have one comment: the authors refer to chemical and XRD analysis in publication [32]. This characteristic should be presented in the text and not a reference to literature, please complete.
Author Response
Review #1:
The authors focused on the effects of preliminary hydrodynamic cavitation of the kaolinite and diaspore suspension for the flotation of these minerals. They investigated the effect of aeration, contact angles as a function of pH and NaOl concentration. They received a distribution of kaolinite from the diaspore. The paper is generally well-written and the structure well-organized. However, I have one comment: the authors refer to chemical and XRD analysis in publication [32]. This characteristic should be presented in the text and not a reference to literature, please complete.
Answer: Thanks for your profound comments about our manuscript and valuable suggestions. In the revised manuscript, we have added XRF and XRD data of the diaspore and kaolinite samples.
Reviewer 2 Report
Comments and Suggestions for AuthorsOverall a well thought out, executed and presented research work on the effect of hydrodynamic cavitation on the properties of (i) collector used, (ii) minerals studies, and (iii) interaction of collector and mineral with the ultimate goal to achieve selectivity and separation in flotation of diaspore and kaolinite. Modern instrumental methods were used to (i) characterize the sodium oleate and its possible changes that occurred after the impact of the hydrodynamic cavitation, (ii) changes in the minerals properties (contact angle and zeta potential), and (iii) NaOl adsorption. The flotation experiments conducted and discussed bring the described study to a complete state, with clear suggestions for improving flotation separation.
I have marked ''average'' for the ''Interest to the readers'' because the presented work is somehow aside from the enumerated journal subjects and probably of the journal readers.
In my opinion, there are some minor technical inaccuracies that need to be corrected. For the convenience of the authors, I am attaching the manuscript file with comments and suggestions therein.
Comments for author File: 
Comments.pdf
Minor editing of English language required
Author Response
1.Please connect the detection services with the other part of the scheme.
Answer: We apologize for the oversight that led to this mistake. In the revised manuscript, we have replaced the scheme flowchart and connected the detection services with the corresponding part of the scheme. If there are any specific nuances or additional details you'd like to include, please feel free to let us know.
- From the figure (Figure 2e) it seems that for example for 1×10-4 M NaOl is about 5%, considerable?
Answer: Thank you for your insightful question. As shown in Fig.2e, under a fixed concentration of NaOl, the reduction in surface tension due to HC treatment appears minimal. However, it is evident that HC treatment induces varying degrees of surface tension reduction under different concentration conditions. It is widely acknowledged that changes in solution surface tension significantly influence interactions between reagents, water, and minerals—enhancing the spreading and wetting of reagents on mineral surfaces. These effects are likely transmitted to the final flotation responses.
- Any comments on the increased viscosity at the highest NaOl concentration?
Answer: Thank you for your insightful suggestions. Our analysis indicates that the measurement data may be influenced by variables such as the concentration of sodium oleate and the shear thinning properties of the solution across various shear rates. It is noteworthy that practical flotation operations often involve stirring speeds around 160s-1. Considering this, we opted to visually compare the apparent viscosity values of the solution under different sodium oleate concentrations and pretreatment conditions at a consistent shear rate (160s-1) to draw qualitative conclusions. The updated graph reflecting these modifications can be found in the revised manuscript.
- It seems that this paragraph meaningfully repeats (at least partially) what was said in the previous two.
Answer: Thank you for your helpful reminder. Our initial aim was to summarize the preceding research and emphasize the impact of HC pretreatment on the apparent contact angles of diaspora and kaolinite, along with their potential mechanisms. Regrettably, certain statements are redundant. We will revise and streamline this section based on your suggestions to enhance its conciseness and precision.
- But your Fig.3 gives higher contact angle increases for diaspore.
Answer: Thank you for your inquiry. It is known that the larger the mineral contact angle, the greater the hydrophobicity and floatability of the mineral surface. This indicates a positive correlation between the size of the mineral contact angle and its flotation behavior. However, research has revealed that the increase in mineral contact angle does not always linearly improve the flotation recovery rate. Studies indicate the existence of a critical contact angle for many minerals. When the mineral surface contact angle is significantly lower or higher than this critical angle, the increase in flotation recovery rate is relatively minimal. Conversely, when the mineral surface contact angle approaches this critical value, even slight changes can lead to significant variations in the flotation recovery rate. Some studies suggest that the critical contact angle for certain oxidized ores falls within the range of 35°-40°. Based on the changes in mineral contact angle and their corresponding recovery rates observed in this study, we hypothesize the following: When the concentration of NaOl is low, the flotation recovery rate of diaspore increases significantly due to the HC treatment, likely because the surface contact angle of diaspore approaches its critical value. Conversely, when NaOl concentration ranges from 0.5 to 1 × 10-4M, the contact angle of kaolinite tends to approach its critical point, resulting in a more pronounced increase in kaolinite flotation recovery rate under HC treatment. In summary, the selective anchoring of newly formed MNBs during the HC process on mineral surfaces, coupled with differential assembly/adsorption of NaOl induced by it, leads to notable differences in the apparent contact angle growth between these two minerals. This phenomenon is likely a primary factor contributing to their distinct flotation behaviors. For simplicity and clarity, we have also made appropriate modifications to the text.
- Unclear or unfinished sentence, please revise it:“It is noteworthy that while we have inferred that, under low NaOl concentration conditions, the remarkable differences in flotation recovery and separation between fine diaspore and kaolinite are most likely due to the selective enhancement in bubble’s mineralization in diaspore case caused by selective surface-anchoring of MNBs.”
Answer: Thank you for your thoughtful question. In the revised manuscript, we have refined the wording of this paragraph to improve its coherence and readability.
- Other details to be modified.
Answer: Thank you very much for your careful review and valuable suggestions. The modifications regarding the minor details mentioned in the manuscript are as follows:
Case 1：Tab.1 depicts the SSA of these two minerals within the -37μm fraction, respectively.
Case 2: However, HC pretreatment of NaOl solution results in a reduction in the movement in negative direction of zeta potential of diaspore particles across the experimental pH range.
Case 3: To determine the actual influence of HC pretreatment on the separation of fine diaspore from fine kaolinite, the flotation separation of minerals mixture under varying NaOl concentration was explored, with the indicators of concentrate shown in Fig.7(b).
Case 4: Obviously, HC pretreatment improves the Al2O3 recovery in concentrate significantly across the experimental NaOl range, achieving maximum enhancement between 0.5×10-4 M and 1×10-4 M NaOl concentration.
Case 5: The annotation of sodium oleate concentration in Figure 7 has been removed.
Case 6: Short-term (3min) HC treatment does not noticeably change the chemical properties of NaOl, but promotes the formation of MNBs in liquids which therefore causes a certain reduction in surface tension and viscosity of NaOl solutions
Overall, we deeply appreciate your constructive suggestions. We have diligently revised the manuscript based on your feedback. While some results remain unexplained at present, your insights have significantly guided our future research direction. In our forthcoming study, we plan to employ advanced visual research methods to elucidate the adsorption and assembly behavior of NaOl in the presence of MNBs on diaspore and kaolinite surfaces. This will provide more compelling evidence to uncover the differential flotation behaviors induced by MNBs on diaspore and kaolinite.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors provided a nice concept for Sodium Oleate Adsorption, however, the manuscript suffers from weak presentation regarding HC. The authors claim that MNBs are role player in this issue, but I cannot see any results regarding MNBs. I believe that the authors misunderstand the existence of microbubbles in HC (MNBs are very difficult to measure in HC) and attributing their role to the separation within the HC is not accurate. My basic comment which specifies the scientific weight of the manuscript is that how the authors measures the role of MNBs in their applications?
There is no any info regarding the cavitation reactor, how this reactor looks like? which flow patterns and thermophysical condition have been employed in this study?
In general the presentation of the results are too weak, I suggest the authors present more data regarding HC occurrence and its effect on the separation mechanism.
Comments on the Quality of English LanguageI have no comment on this.
Author Response
The authors provided a nice concept for sodium oleate adsorption, however, the manuscript suffers from weak presentation regarding HC. The authors claim that MNBs are role player in this issue, but I cannot see any results regarding MNBs. I believe that the authors misunderstand the existence of microbubbles in HC (MNBs are very difficult to measure in HC) and attributing their role to the separation within the HC is not accurate. My basic comment which specifies the scientific weight of the manuscript is that how the authors measure the role of MNBs in their application?
There is no any info regarding the cavitation reactor, how this reactor looks like? Which flow patterns and thermophysical condition have been employed in this study?
In general, the presentation of the results are too weak, I suggest the authors present more data regarding HC occurrence and its effect on the separation mechanism.
Comments on the Quality of English Language? I have no comment on this.
Answer: Thank you for your insightful questions. I am prepared to delve into the topic from several perspectives. Firstly, addressing the generation of MNBs during the HC process, while some debate persists, mounting research and evidence increasingly suggest that MNBs are indeed produced [1]. These newly generated tiny bubbles possess unique properties compared to conventional bubbles, notably exhibiting strong stability and the ability to persist in the liquid phase for extended periods, often hours or more. These characteristics enable non-instantaneous detection. Researchers have identified MNBS and explored their fundamental physicochemical properties using various advanced techniques such as atomic force microscopy, scanning electron microscopy, attenuated infrared spectroscopy, and dynamic light scattering [2, 3]. Notably, nanoparticle tracking analysis has gained prominence in recent years for assessing the morphology and concentration size distribution of newly formed MNBS in HC processes [4, 5]. Moreover, utilizing consistent experimental setups, our previous studies have successfully detected MNBs and scrutinized their properties [6, 7]. This comprehensive approach unequivocally demonstrates our experimental system's capability to generate MNBs, validating their detectability and confirming their distinct properties.
Simultaneously, MNBs flotation technology has been extensively researched. The selective anchoring and adsorption of MNBs at hydrophobic interfaces can induce significant modifications in the properties of multiphase interfaces, such as minerals, reagents, and flotation bubbles, thereby altering the flotation behavior of minerals [8]. Common research methods for elucidating interactions involving minerals and pharmaceutical MNBs include atomic force microscopy, laser confocal microscopy, optical microscopy, and attenuated fluorescence microscopy. Some studies also analyze changes in the physicochemical properties of the system due to MNBs interactions with minerals/agents [9], indirectly revealing these interactions through surface tension testing, dynamic potential testing, floc property testing [10], and other methods [11]. These studies conclusively demonstrate the applicability of various modern research methods in exploring MNBs in mineral flotation. The methods are diverse, the research process is feasible, and the results are reliable.
Fig.1 and Fig.2 depict the physical structure and geometric parameters of the Venturi-type cavitation generator utilized in this study. Relevant information has been previously published [12]. The cavitation tests are conducted under normal temperature and pressure conditions. According to Bernoulli's principle, the flow velocity at the throat of the Venturi tube is notably high during testing and exists in a turbulent state.
Fig.1 Physical map of cavitation tube
Fig.2 Schematic diagram of cavitation pipe throat structure
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsI have no further comment.
Author Response
Thank you for your advice on our manuscript!
